Transforming from boy into a girl is what connects these anime the most. Senou Natsuru from Kämpfer have to do it against his will, but for Mitsuka Souji from Ore, Twintails ni Narimasu. it's just a side-effect of using battle-suit. Both shows have elements of mahō-shōjo, romance, comedy and ecchi, and Gonna be the Twin-Tails!! has also some elements of mecha.

* In both shows, tha main male character transforms into a girl.
* The main character have a childhood friend and the Student council president joins to their team.
* Both have some fanservice. (Twintail less than Kampfer)
* Similar genres

Both are amazing comedies with a gender-bent main character, who has to learn to deal with living as a girl. Kampfer is more full-on with this, as the main takes a while to learn to control the transformations, while TailRed mostly controls his transformations...